1. Field of the Invention
The present invention relates to negative-type planographic printing plate. More particularly, the invention relates to a negative-type planographic printing plate having, disposed on a support, at least a recording layer comprising a heat-mode compatible, negative-type image recording material usable for a planographic printing plate precursors which is capable of directly forming a printing plate, that is, capable of direct printing plate production by performing scanning with infrared ray lasers in accordance with digital signals outputted from a computer or the like.
2. Description of the Related Art
Heretofore, as for systems for performing such direct printing plate production in accordance with digital data outputted from a computer, systems for direct printing plate production by:
(1) electrophotography;
(2) photopolymerization by exposure with a laser emitting a blue or green light;
(3) a laminate comprising a silver halide superposed on a photosensitive resin;
(4) a silver salt diffusion transfer process; and the like have been proposed.
However, in the system (1) which utilizes the electrophotography, an image forming process comprising charging process, exposure, development and the like is troublesome and complicated and large scaled apparatus is required. In the system (2) which utilizes photopolymerization, a plate sensible to blue or green lights are used. Therefore it becomes difficult to handle the plates in a lighted room. In the systems (3) and (4), the silver halide is used whereby a process comprising development becomes complicated and, further, there is a drawback in that silver is contained in waste water of treatments.
With remarkable developments of lasers in recent years, in particular solid state lasers and semiconductor lasers which emit an infrared ray particularly in a wavelength range from 760 nm to 1200 nm, and which have a high output in power and are compact in size have become readily available. Such lasers are extremely effective as a light source for recording in performing the direct printing plate production in accordance with the digital data outputted from a computer or the like. However, since a multiplicity of practically useful photosensitive recording materials have sensitivity in visible light range which is in a wavelength of 760 nm or less, so, image recording can not be performed by such infrared ray lasers. Accordingly, there has been a demand for a material on which an image can be recorded by the infrared ray lasers.
An image recording material, comprising an onium salt, a phenolic resin, and a spectral sensitizer, on which an image can be recorded by the infrared ray lasers, is disclosed in U.S. Pat. No. 4,708,925. This image recording material is a positive-type image recording material that utilizes a inhibition of dissolution in a developer by the onium salt and the phenolic resin So, this positive-type image recording material is different from the negative-type one according to the present invention.
On the other hand, as for negative-type image recording materials, a recording material comprising an infrared ray absorbing agent, an acid generating agent, a resol resin and a novolak resin is disclosed in U.S. Pat. No. 5,340,699. However, such negative-type image recording materials require heat treatment for image forming after a laser exposure is performed whereupon there has been a demand for the negative-type image recording material which does not require the heat treatment after the exposure is performed.
For example, the recording material which can be addtion-polymerized and which does not require the heat treatment after exposure for image formation is performed is described in Japanese Patent Application Publication (JP-B) No. 7-103171. This material comprises an addition-polymerizable compound that contains a cyanine dye having a specific structure, a iodonium salt and an ethylenically unsaturated double bond. However, in this image recording material, particularly storability of dyes is decreased and an unexposed area thereof becomes hard to be dissolved in a developer depending on environmental conditions of storage thereof. Hence, there has been a problem in that discrimination between the unexposed area and an exposed area is insufficient, a non-image area is liable to be imparted with a stain and the like.